首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   1195篇
  免费   318篇
  国内免费   99篇
化学   415篇
晶体学   4篇
力学   52篇
综合类   3篇
数学   70篇
物理学   754篇
综合类   314篇
  2024年   10篇
  2023年   14篇
  2022年   35篇
  2021年   48篇
  2020年   33篇
  2019年   36篇
  2018年   53篇
  2017年   75篇
  2016年   60篇
  2015年   62篇
  2014年   104篇
  2013年   114篇
  2012年   93篇
  2011年   97篇
  2010年   73篇
  2009年   95篇
  2008年   84篇
  2007年   68篇
  2006年   69篇
  2005年   70篇
  2004年   36篇
  2003年   38篇
  2002年   34篇
  2001年   28篇
  2000年   24篇
  1999年   18篇
  1998年   14篇
  1997年   12篇
  1996年   17篇
  1995年   16篇
  1994年   12篇
  1993年   12篇
  1992年   12篇
  1991年   4篇
  1990年   12篇
  1989年   5篇
  1988年   7篇
  1987年   4篇
  1986年   4篇
  1985年   7篇
  1984年   1篇
  1981年   2篇
排序方式: 共有1612条查询结果,搜索用时 125 毫秒
1.
物流系统容错设计方法   总被引:2,自引:0,他引:2  
在相关理论的指导下,提出了物流容错技术的基本概念,论述了常见的系统故障、典型的容错设计方法和故障检测手段,讨论了物流容错技术的应用前景和发展方向。  相似文献   
2.
A series of low density polyethylene systems has been studied with respect to structural evolution and short-term dielectric breakdown behaviour. All materials were based upon a single polymer, that is commonly used in high voltage applications, but with different additives. In all three of these systems, multiple melting transitions were observed, as a result of molecular fractionation effects during crystallization. In the virgin polymer, a space-filling banded spherulitic morphology was found to develop at low temperatures (102 °C and below) whereas, at higher temperatures, only a few isolated axialites were observed. Inclusion of the antioxidant resulted in greatly increased nucleation densities, such that, at low temperatures, no evidence of spherulitic organisation remained. At higher temperatures, sheaf-like lamellar aggregates developed, which were much smaller and much more numerous than in the case of the virgin polymer. Further addition of dicumyl peroxide (DCP) resulted in the rapid formation of a crosslinked network at 200 °C. Some crosslinking also occurred at 150 °C, but over a much longer timescale. Where extensive crosslinking occurred prior to crystallization, the resulting gel inhibited structural development, such that only a few small, isolated sheaves were able to form at 102 °C. In view of the principal application area of this material, the breakdown strength of each of the above systems was then measured and the whole data set was analysed statistically. When structural factors were considered alongside the statistics, no clear trends emerged to indicate that either the compositional or morphological variations were reflected in the short-term electrical failure processes.  相似文献   
3.
In different regimes of exposure of metals to pulsed laser radiation, we show the role played by the liquid-drop phase formed from the target material in a laser-induced erosion plume due to bulk vaporization, in the dynamics of this plume. For some metals, the ranges of power densities of the acting laser radiation, at which the condensed-phase particles influence the passage of laser radiation to the target surface, have been determined experimentally. The mechanism of realization of a low-threshold breakdown has been revealed.  相似文献   
4.
To prevent cyanobacterial bloom in eutrophic water by ultrasonic method, ultrasonic irradiations with different parameters were tested to inhibit Spirulina platensis from growth. The experimental result based on cyanobacterial growth, chlorophyll a and photosynthetic activity showed that, the ultrasonic irradiation inhibited cyanobacterial proliferation effectively, furthermore the inhibition effectiveness increased in the order: 200 kHz>1.7 MHz>20 kHz and became saturated with the increased power. The inhibition mechanism can be mainly attributed to the mechanical damage to the cell structures caused by ultrasonic cavitation, which was confirmed by light microscopy and differential interference microscopy. The optimal frequency of 200 kHz in cavition and sonochemistry was also most effective in cyanobacterial growth inhibition. The higher frequency of 1.7 MHz is weaker than 20 kHz in cavitation, but has more effective inhibition because it is nearer to the resonance frequency of gas vesicle. The inhibition saturation with ultrasonic power was due to the ultrasonic attenuation induced by the acoustic shielding of bubbles enclosing the radiate surface of transducer.  相似文献   
5.
工程项目结构分解及其编码是项目管理的基础工作。目前该方法的应用缺乏统一的标准和规范,影响其应用效果。针对这种情况,提出该方法的优化途径--分解对象标准化,分解步骤统一化,分解规则规范化。进而指出该方法新的应用领域,特别是在项目管理信息集成方面,及对提高工程项目管理水平所起的作用。  相似文献   
6.
模拟和验证了一种低成本的,以标准CMOS工艺为基础,无需对原工艺流程进行改动的高压工艺技术。讨论了低压器件中的各种击穿机理,相应提出了高压器件中所做出的改进,列举了该工艺技术中所用的特殊版图;对此工艺的应用性进行了二维的工艺和器件模拟;将模拟结果与实际测试结果进行了比较,验证了这种高压工艺技术的实用性。  相似文献   
7.
赵毅  万星拱 《物理学报》2006,55(6):3003-3006
用斜坡电压法(Voltage Ramp, V-ramp)评价了0.18μm双栅极 CMOS工艺栅极氧化膜击穿电量(Charge to Breakdown, Qbd)和击穿电压(Voltage to Breakdown, Vbd). 研究结果表明,低压器件(1.8V)的栅极氧化膜(薄氧)p型衬底MOS电容和N型衬底电容的击穿电量值相差较小,而高压器件(3.3V)栅极氧化膜(厚氧)p衬底MOS电容和n衬底MOS电容的击穿电量值相差较大,击穿电压测试值也发现与击穿电量 关键词: 薄氧 可靠性 击穿电压 击穿电量  相似文献   
8.
以HG145型摩擦焊接机为例,介绍了利用梯形图分析PLC控制系统故障的方法。  相似文献   
9.
分析了柱形导体对均强电场的影响并以此为依据说明了有柱形凸起的高压电容器易击穿的原因是最凸部场强为远离凸部场强的 2倍。  相似文献   
10.
The Nd:YAG laser-induced breakdown of 20 μm glass microspheres was investigated using time-resolved optical shadow and Schlieren images. Time-resolved imaging showed the location of the initial breakdown and the shockwave motion over its first 400 μm of expansion. Measured shockwave velocities were in the range of 1–10 km/s and showed a linear dependency on laser fluence within 30 ns.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号